This invention relates to agricultural implements, and more specifically, to agricultural implements used in ground breaking procedures such as subsoil ripping, plowing or the like.
Typically, tools such as plow blades or ripper shanks are secured to a frame which traverses the underlying terrain when pulled by a tractor or the like. The blades or shanks enter the underlying terrain and as the frame is moved thereover, perform the desired ground breaking operation.
During such movement, so long as only soil is encountered, no problem exists. However, not infrequently an obstacle such as a buried rock or the like of relatively large size is encountered by the tool which is impossible for the tool to dislodge. When such an obstacle is encountered, severe stresses are placed on the implement and may even be transmitted to the implement pulling vehicle. Such shocks can severely damage the equipment if no provision is made to avoid them.
Thus, it has been common to pivotally mount the tool on the frame for movement between a forward, ground breaking position and a rearward inoperative position whereat it may slip over the obstacle it has encountered. Releasable means are utilized to maintain the tool in its forwardmost position in normal operation and to release the tool for movement to its rearward position when some predetermined amount of resistence in excess of that normally encountered appears as, for example, when hitting an obstacle.
In general, the releasable means have taken on two different forms. In one form, a spring biased trip system is utilized. In another form, fracturable elements as shear pins have been utilized.
Spring trip linkages typically require considerably more components than shear pin type systems with a consequence that they are more expensive. The shear pin type system requires more effort to reengage after they have been tripped and require the replacement of the sheared pin.
Moreover, because a shear pin is typically disposed within two or more aligned bores on relatively movable components and sheared by a scissors-like action, the resulting deformation of the shear pin may make it extremely difficult to remove the remnants of the shear pin from the bore after shearing in order to replace it.